The present invention relates to a device for determining the position and orientation of a movable object. The invention further relates to a corresponding method.
Determining the position of objects, for example vehicles, robots and the like, in an x-direction and/or y-direction has been long established practice. For example, using a GPS to determine the position of vehicles is known, but is only possible if a corresponding receiver can receive signals from the associated satellites. This is often difficult in interior spaces, so that other methods and devices are resorted to there.
For example, determining the position of objects or motor vehicles in interior spaces is necessary for industrial vehicles (forklifts, rack systems, etc.) to measure and control mobile robots, and for virtual studios to remotely operate cameras. In all applications, the position must be known almost at all times. In addition to the position of the vehicle in a two-dimensional plane, its spatial orientation of often an essential criterion. Orientation in this sense refers to the rotation of the object or vehicle around its vertical axis, for example the alignment or pivoting angle of a camera in a television studio. Not just the position of the vehicle (on which the camera is located) is important for this application, but also its twisting or the twisting of the camera around the vertical axis constitutes important information, since the latter significantly influences the image to be recorded. It is also pivotal that the position be known not just at rest, but also in transit or motion. Therefore, the position and orientation must be calculated in real time.
EP 1 455 253 A2 discloses a system for determining the absolute position, for example a camera. The system is essentially based upon covering a studio floor with circular markers that each exhibit an individual pattern. The position of the individual markers is known. The camera has a sensor that takes 20 images/second of the patterns on the studio floor, wherein the markers are used to detect the absolute position. It is here essential that not just one marker be evaluated, but also those markers that surround the latter.
The simultaneous recording of several adjacent markers also enables the unambiguous allocation of a central marker. In addition to recognizing the position, rotation can also be determined from the image of a sensor or two sensors. This system has proven itself from the standpoint that it enables a highly accurate determination of position at any time. However, the disadvantage has had to do with the special configuration of the studio floor. The pattern yielded by the markers is frequently viewed as disruptive and disadvantageous, so that the system is often not put to use. Another key disadvantage is that such a floor covering does not completely disappear when the real image is blended with a virtual image, which is frequently the case in studio productions, which does occur, for example, in the remainder of a blue studio. In addition, the markers get dirty over time, which can result in erroneous information. For this reason, the studio floor must be kept very clean.
In addition, applying the specially imprinted floor, e.g., made of PVC, on-site is associated with considerable expense. It is virtually impossible to outfit an existing studio with a new studio floor, since all equipment and furniture must first be removed for this purpose. Further, the floor imprinted with markers must be installed identically given the fixed position of the individual markers.
Also known are odometric systems, in which the position of a vehicle is determined by observing its wheels. However, the disadvantage to this fundamental navigation method for land-bound vehicles of all kind is that the position measurement is subject to a plurality of influencing variables that often result in too great a deviation from reality. These include wheel geometry (runout, wear), composition of the ground (unevenness, dirt), chassis geometry (play, erroneous measurement of wheel distances and steering gear) and the vehicle weight (uneven distribution of weight; greater load and deformation on individual wheels).
The biggest error stems from the fact that the wheel “slips” when driving through a curve; the rigid wheel expands vertically to the traveling direction, and the radius of the inner edge of the wheel differs relative to the outer edge in the case of a curve. In addition, the wheel does not precisely follow the curve trajectory, but rather most often slips more straight ahead.
All of these errors are incorporated in the position difference that is added to the last known position. As a result, the errors add up with each measuring step, leading to an ever-growing deviation during a more prolonged measurement. This deviation in odometric position calculation is virtually impossible to avoid, even if all error influences are minimized. In particular, it is necessary to drive the vehicles to a known initial position at regular intervals, so as to begin determining the position again from there. This is necessary in particular if the vehicle was often moved back and forth or drove through curves, since the error frequency increases during such movements.
GB 2259823 A describes another method for absolute position determination. In this method, the walls of a room are provided with a plurality of reflectors having an unambiguous code. The position of each individual reflector is known, and the code allows it to be unambiguously allocated. Situated in proximity to the camera is a light source, which shines on the reflectors, so that a sensor, e.g., a camera, can detect the reflected light or signal. the position can be determined relatively precisely based on the recorded and unambiguously allocated reflected signals However, the disadvantage to this method is that many reflectors have to be present, and that the reflectors can often not be uniformly arranged because they are covered by objects such as studio furniture or doors, other cameras or camera personnel. Finally, the reflectors affixed to the walls might also subsequently become obscured by persons or other objects, which in this relatively sensitive system leads to errors or calculation deficiencies.